Menstrual cycle variability and the likelihood of achieving pregnancy

Longitudinal associations between women's cycle characteristics and sexual motivation using Flo cycle tracking data

In the current research, we used data from a sample of 16,327 menstrual cycle tracking app users to examine the association between menstrual cycle characteristics and sexual motivation tracked over 10 months of app use. Guided by past work that finds links between menstrual cycle characteristics related to conception risk and sexual motivation, we found that (a) between-women, shorter (r = - 0.04, p = 0.007), more regular cycles predicted small increases in sexual motivation (r = - 0.04, p = 0.001); (b) within-women, shorter cycles predicted greater sexual motivation that month (r = - 0.04, p < 0.001) and (c) the next month (βs: - 0.10 to - 0.06, ps < 0.001), but (d) changes in sexual motivation did not reliably precede changes in cycle length (βs: - 0.01 to 0.02, ps > 0.15). Within-woman analyses also revealed that (e) shorter cycles were followed by more frequent reports of fatigue (β = - 0.06, p < 0.001), insomnia (β = - 0.03, p < 0.001), and food cravings (β = - 0.04, p < 0.001). Together, results suggest that menstrual cycles characteristics and sexual motivation may covary together in ways that reflect changing investments in reproduction. Small effect sizes and lack of experimental control warrant cautious interpretations of results.

Associations of chronotype and insomnia with menstrual problems in newly employed nurses at university hospitals in the Republic of Korea

Background

Dysmenorrhea and menstrual cycle changes occur in women working shifts. Circadian rhythm disruption and sleep disturbances associated with shift work leads to health problems. We identified chronotypes and the occurrence of insomnia among newly employed university hospital nurses and investigated the association of these factors with menstrual problems.

Methods

We conducted pre-placement health examinations for shift workers using self-reported questionnaires between 2018 and 2020. A total of 463 nurses were included in the study. Sociodemographic data, shift work experience, and information on insomnia were collected from health examination data. In addition, details regarding chronotype, dysmenorrhea, irregular and abnormal menstrual cycles, amenorrhea, and contraceptive use were obtained from the questionnaire. Multiple logistic regression analysis was performed to study the association between chronotype, insomnia, and menstrual problems after controlling for age, body mass index, contraceptive use, amenorrhea, and prior shift work.

Results

The prevalence rates of dysmenorrhea, irregular menstrual cycles, and longer menstrual cycles were 23.8%, 14.9%, and 4.1%, respectively. The risk of dysmenorrhea increased in the evening-type (odds ratio [OR]: 3.209; 95% confidence interval [CI]: 1.685-6.113) and those with insomnia (OR: 1.871; 95% CI: 1.074-3.261). Additionally, the risk of an irregular menstrual cycle (OR: 2.698; 95% CI: 1.167-6.237) increased in the evening-type, and the risk of a longer menstrual cycle (OR: 4.008; 95% CI: 1.354-11.864) increased in individuals with insomnia.

Conclusions

Our findings suggest that dysmenorrhea is promoted in the evening-type and insomnia individuals. There may be an increased risk of irregular menstrual cycles among evening-type nurses and an increased risk of longer menstrual cycles among those with insomnia. Therefore, factors such as evening-type and insomnia should be considered for the prevention of menstrual problems in women performing shift work.

Menstrual cycle length variation by demographic characteristics from the Apple Women's Health Study

Menstrual characteristics are important signs of women's health. Here we examine the variation of menstrual cycle length by age, ethnicity, and body weight using 165,668 cycles from 12,608 participants in the US using mobile menstrual tracking apps. After adjusting for all covariates, mean menstrual cycle length is shorter with older age across all age groups until age 50 and then became longer for those age 50 and older. Menstrual cycles are on average 1.6 (95%CI: 1.2, 2.0) days longer for Asian and 0.7 (95%CI: 0.4, 1.0) days longer for Hispanic participants compared to white non-Hispanic participants. Participants with BMI ≥ 40 kg/m² have 1.5 (95%CI: 1.2, 1.8) days longer cycles compared to those with BMI between 18.5 and 25 kg/m². Cycle variability is the lowest among participants aged 35-39 but are considerably higher by 46% (95%CI: 43%, 48%) and 45% (95%CI: 41%, 49%) among those aged under 20 and between 45-49. Cycle variability increase by 200% (95%CI: 191%, 210%) among those aged above 50 compared to those in the 35-39 age group. Compared to white participants, those who are Asian and Hispanic have larger cycle variability. Participants with obesity also have higher cycle variability. Here we confirm previous observations of changes in menstrual cycle pattern with age across reproductive life span and report new evidence on the differences of menstrual variation by ethnicity and obesity status. Future studies should explore the underlying determinants of the variation in menstrual characteristics.

Preconception menstrual cycle disorder and antenatal depression: a cross-sectional study with prerecorded information

OBJECTIVES

This study aimed to evaluate the association between pre-pregnancy menstrual cycle characteristics (i.e. cycle-length variability and cycle length) and antenatal depression.

METHODS

This study retrieved the data from the baseline survey of the randomized controlled trial with pregnant women at 16-20 weeks gestation who used a pregnancy tracking app. The antenatal depression was assessed using the Edinburgh Postnatal Depression Scale (EPDS) at 16-20 weeks gestation, and the cutoff point of 10/11 was adopted. Pre-conceptional menstrual cycle information was obtained via a prerecorded period tracking app. Cycle-length variability was defined as the average difference in the lengths between cycles, dichotomized into regular (≤6 days) and irregular (>6 days). Cycle length was coded as a categorical variable: <25 days, 25-26 days, 27-29 days (regular), 30-31 days, 32-33 days, and 34+ days. The associations of cycle disorders with EPDS scores were examined using regression analysis and a multiple logistic regression model adjusted for covariates.

RESULTS

The total of 3473 participants were analyzed in this study. Irregular cycle variability (>6 days) was significantly associated with high EPDS scores (adjusted: standardized beta = 0.049, p = 0.003) and with high cutoff EPDS scores (over 11) (adjusted OR = 1.40 [1.02-1.94], p = 0.038) but not with cycle length.

CONCLUSION

Irregular menstrual cycle before pregnancy was associated with depression during pregnancy. The health of the menstrual cycle during preconception needs to be further explored to promote healthy maternal mental health.

The impact of workplace psychosocial factors on menstrual disorders and infertility: a protocol for a systematic review and meta-analysis

INTRODUCTION

Workplace environment, especially psychosocial factors at work such as job strain, workplace social support, and shift work, may affect the menstrual abnormalities and fertility of female workers. However, the association between psychosocial factors at work and menstrual abnormalities or fertility is not well understood. To address this relationship, we will conduct a systematic review and a meta-analysis of the literature that has utilized a longitudinal or prospective cohort design.

METHODS AND ANALYSIS

The inclusion criteria for this systematic review and meta-analysis are defined as follows: (P) adult female workers (over 18 years old), (E) the presence of adverse psychosocial factors at work, (C) the absence of adverse psychosocial factors at work, and (O) any menstrual cycle disorders, menstrual-related symptoms, or fertility. The MEDLINE, Embase, PsycINFO, PsycArticles, and Japan Medical Abstracts Society electronic databases will be used to search for published studies. The statistical synthesis of the studies included in the meta-analysis will be conducted to estimate pooled coefficients and 95% CIs. For the main analysis, we will synthesize measures of association between psychosocial factors at work and menstrual-related disorders/symptoms. At least three eligible studies will have to be gathered to conduct a meta-analysis; otherwise (i.e., if only one or two studies will be eligible and included), the results will be presented in a narrative table. We will use the Risk of Bias in Non-randomized Studies of Interventions (ROBINS-I) to determine the quality of selected studies. To assess meta-bias, Egger's test, along with a funnel plot, will be used to check for publication bias. Lastly, we will examine heterogeneity using the χ² test with Cochran's Q statistic and I².

ETHICS AND DISSEMINATION

The results and findings will be submitted and published in a scientific peer-reviewed journal and will be disseminated broadly to researchers and policymakers interested in the translatability of scientific evidence into good practices.

SYSTEMATIC REVIEW REGISTRATION

The study protocol was registered at the UMIN registry (registration number: UMIN000039488). The registration date is on 14 Feb 2020. URL: https://upload.umin.ac.jp/cgi-bin/ctr/ctr_view_reg.cgi?recptno=R000044704.

Factors associated with regularity and length of menstrual cycle: Korea Nurses’ Health Study

Background

Menstrual cycle characteristics are linked to reproductive function and long-term health outcomes. This study aimed to evaluate menstrual cycle patterns, characterized by regularity and length, and associated factors among women in the Korea Nurses’ Health Study.

Methods

A total of 9335 premenopausal women aged 22–45 years were included in this cross-sectional study. Regularity and length of menstrual cycles were self-reported, and their associations with reproductive, lifestyle, and occupational factors were examined using binomial and multinomial logistic regression models. Adjusted least-square means of menstrual distress, depressive symptoms, stress, fatigue, anxiety, and sleep problems were estimated according to menstrual cycle characteristics using generalized linear models.

Results

Twenty-one percent of nurses reported having irregular menstrual cycles (variability > 7 days). Ten percent, 64%, and 26% had menstrual cycle length of < 26, 26–31, and 32–50 days, respectively. Variability and length of cycles decreased with age and increased with age at menarche. Parous women showed low tendency of irregular cycles. Women with body mass index (BMI) > 25 kg/m² had higher odds of irregular (odds ratio [OR] 1.68; 95% confidence interval [CI] 1.40–2.03) and long cycles (OR 1.31; 95% CI 1.08–1.58) than those with BMI 18.5– < 23 kg/m². Irregular cycles were less common in women performing vigorous physical activity, but more common in those with prolonged standing or frequent heavy lifting at work. Frequent rotating night shift was associated with irregular cycles among nulliparous women. Levels of menstrual and premenstrual distress, depressive symptoms, perceived stress, physical and mental fatigue, anxiety, and sleep problems were higher in women with irregular cycles than in those with regular cycles (p < 0.001, each).

Conclusions

The study suggests that irregular and long menstrual cycles are associated with reproductive, lifestyle, and occupational factors; also with menstrual distress and perceived health status. Our findings contribute to a better understanding of potential risk factors for menstrual dysfunction, and thus, may help improve women’s health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12905-022-01947-z.

Does an association exist between menstrual cycle length within the normal range and ovarian reserve biomarkers during the reproductive years? A systematic review and meta-analysis

BACKGROUND

Regular menstrual cycling during the reproductive years is an indicator of spontaneous ovulation but sometimes falsely perceived as an indicator of preserved fertility. In contrast, menstrual cycle shortening, a physiologic occurrence preceding the menopausal transition, is not usually perceived as an indicator of decreased ovarian reserve in the general population.

OBJECTIVE AND RATIONALE

The individual decrease in menstrual cycle length (MCL) might represent a sensitive biomarker of diminishing ovarian reserve. The aim of this systematic review and meta-analysis is to examine the possible association between MCL in regularly cycling women (21-35 days) and ovarian reserve tests (ORT), fecundability in natural cycles and IVF outcomes.

SEARCH METHODS

An electronic database search employing PubMed, Web of Science, Trip, EBSCO, ClinicalTrials.gov and the Cochrane library was performed to identify research articles, only on human, published between January 1978 and August 2019. Search terms were pregnancy OR fertility OR fecundity OR fecundability, anti-Müllerian hormone OR AMH OR antral follicle count OR AFC OR ovarian reserve OR ovarian reserve test, in vitro fertilization OR ART OR assisted reproductive therapy OR assisted reproductive treatment OR assisted reproductive technology OR IVF OR ICSI, menstrual cycle length OR menstrual cycle characteristics. We combined these terms to complete the search. All prospective and retrospective studies exploring an association between MCL and proxies of ovarian reserve were included. The exclusions included studies of PCOS, ovarian failure, oral contraception treatment, prior chemotherapy and/or radiotherapy or ovarian surgery. The Newcastle-Ottawa scale was used to assess the quality of studies that were eligible for meta-analysis.

OUTCOMES

Eleven studies were eligible for meta-analysis, including 12 031 women. The included studies had a low risk of bias. Short MCL (21-27 days) was associated with lower ORT values as compared to normal (28-31 days), long (32-35 days) and all other (28-35 days) MCL sets. The estimated weighted mean difference (WMD) of AMH level was -1.3 ng/mL (95% CI: -1.75 to -0.86, P < 0.001) between the short and normal MCL sets. The estimated WMD of AFC values was -5.17 (95% CI: -5.96 to -4.37, P < 0.001) between the short and normal MCL sets. The weighted overall odds ratio (OR) of fecundability in natural cycles between women with short versus normal MCL sets was statistically significant (overall OR 0.81; 95% CI 0.72-0.91, P < 0.001). In the IVF setting, fewer oocytes were retrieved in short MCL in comparison to normal, long and all other MCL sets, with an estimated WMD of -1.8 oocytes (95% CI: -2.5 to -1.1, P < 0.001) in the short versus normal MCL sets. The weighted overall OR of clinical pregnancy rate between women with short versus all other MCL sets was statistically significant (overall OR 0.76; 95% CI: 0.60 to 0.96, P = 0.02). Low levels of heterogeneity were found in most meta-analyses of MCL and qualitative ovarian reserve biomarkers, while heterogeneity was high in meta-analyses performed for quantitative measures.

WIDER IMPLICATIONS

MCL in regularly cycling women is closely related to ovarian reserve biomarkers during the reproductive years. A short MCL, as compared to normal, is significantly associated with lower ORT values, reduced fecundability and inferior IVF outcomes, independent of age. The results imply that short MCL may be a sign of ovarian aging, combining the quantitative and qualitative facets of ovarian reserve. Educational efforts ought to be designed to guide women with short MCL at a young age, who desire children in the future, to seek professional counselling.

Exposure to Organophosphate Pesticides and Menstrual Cycle Characteristics in Chinese Preconceptional Women

Organophosphates (OPs) are the most heavily used pesticides in China. The Chinese population, including preconceptional women, is highly exposed, yet little is known regarding the associations between OP exposure and menstruation in humans. We conducted a cross-sectional analysis in women preparing for pregnancy to investigate the relationship between biomarkers of OP exposure and menstrual cycle characteristics. From 2013 to 2015, 627 women visiting free preconception-care clinics at 2 maternity hospitals in Shanghai, China, were included. Information on menstrual cycle characteristics was obtained through questionnaires. OP exposure was assessed by measuring urine concentrations of 6 dialkylphosphate metabolites (dimethylphosphate, dimethylthiophosphate, dimethyldithiophosphate, diethylphosphate, diethylthiophosphate, and diethyldithiophosphate). The relationship between concentrations of dialkylphosphate metabolites and menstrual cycle characteristics was analyzed using multiple linear regression models and logistic regression models. Log-transformed levels of diethyl phosphate metabolites (the sum of diethylphosphate and diethylthiophosphate levels) were related to a higher risk of irregularity of menstrual cycles (adjusted odds ratio = 2.36, 95% confidence interval: 1.28, 4.34). Subjects with a higher concentration of diethyl phosphate metabolites (log-transformed) had a shorter duration of menstrual bleeding (adjusted β = -0.33, 95% confidence interval: -0.64, -0.02). The findings suggest that OP exposure may be associated with alterations in menstrual function in preconceptional women.

Urinary Phytoestrogens and Relationship to Menstrual Cycle Length and Variability Among Healthy, Eumenorrheic Women

Context

Phytoestrogens may influence fecundability, although biological mechanisms remain elusive. Since it is hypothesized that phytoestrogens may act through influencing hormone levels, we investigated associations between phytoestrogens and menstrual cycle length, a proxy for the hormonal milieu, in healthy women attempting pregnancy.

Design

A population-based prospective cohort of 326 women ages 18 to 40 with self-reported cycles of 21 to 42 days were followed until pregnancy or for 12 months of attempting pregnancy.

Methods

Urinary genistein, daidzein, O-desmethylangolensin, equol, enterodiol, and enterolactone were measured upon enrollment. Cycle length was determined from fertility monitors and daily journals. Linear mixed models assessed associations with continuous cycle length and were weighted by the inverse number of observed cycles. Logistic regression models assessed menstrual regularity (standard deviation > 75th vs ≤ 75th percentile). Models were adjusted for age, body mass index, race, creatinine, exercise, supplements, lipids, lead, cadmium, cotinine, parity, alcohol, and other phytoestrogens.

Results

Individual phytoestrogens were not associated with cycle length, although total phytoestrogens were associated with shorter cycles (-0.042 days; 95% confidence interval [CI], -0.080 to -0.003, per 10% increase). Each 1 nmol/L increase in enterolactone (odds ratio [OR] 0.88; 95% CI, 0.79-0.97) and total lignans (OR 0.85; 95% CI, 0.76-0.95) was associated with reduced irregularity, and each 1 nmol/L increase in genistein with irregularity (OR 1.19; 95% CI, 1.02-1.38).

Conclusion

Phytoestrogens were not meaningfully associated with cycle length but may be associated with menstrual regularity, among women with self-reported regular cycles. These results highlight differences between isoflavones and lignans and are reassuring for women attempting pregnancy.

Individual and cyclic estrogenic profile in women: Structure and variability of the data

The concentration of estrogens in the body fluids of women is highly variable, due to the menstrual cycle, circadian oscillations, and other physiological and pathological causes. To date, only the cyclic fluctuations of the principal estrogens (estradiol and estrone) have been studied, with limited outcome of general significance. Aim of the present study was to examine in detail the cyclic variability of a wide estrogens' panel and to interpret it by multivariate statistics. Four estrogens (17α-estradiol, 17β-estradiol, estrone, estriol) and eleven of their metabolites (4-methoxyestrone, 2-methoxyestrone, 16α-hydroxyestrone, 4-hydroxyestrone, 2-hydroxyestrone, 4-methoxyestradiol, 2-methoxyestradiol, 4-hydroxyestradiol, 2-hydroxyestradiol, estriol, 16-epiestriol, and 17-epiestriol) were determined in urine by a gas chromatography - mass spectrometry method, which was developed by design of experiments and fully validated according to ISO 17025 requirements. Then, urine samples collected every morning for a complete menstrual cycle from 9 female volunteers aged 24-35 years (1 parous) were analysed. The resulting three-dimensional data (subjects × days × estrogens) were interpreted using several statistical tools. Parallel Factor Analysis compared the estrogen profiles in order to explore the cyclic and inter-individual variability of each analyte. Principal Component Analysis (PCA) provided clear separation of the sampling days along the cycle, allowing discrimination among the luteal, ovulation, and follicular phases. The scores obtained from PCA were used to build a Linear Discriminant Analysis classification model which enhanced the recognition of the three cycle's phases, yielding an overall classification non-error rate equal to 90%. These statistical models may find prospective application in fertility studies and the investigation of endocrinology disorders and other hormone-dependent diseases.

Joint analysis of longitudinal and survival data measured on nested timescales by using shared parameter models: an application to fecundity data

We consider the joint modelling, analysis and prediction of a longitudinal binary process and a discrete time-to-event outcome. We consider data from a prospective pregnancy study, which provides day level information regarding the behaviour of couples attempting to conceive. Reproductive epidemiologists are particularly interested in developing a model for individualized predictions of time to pregnancy (TTP). A couple's intercourse behaviour should be an integral part of such a model and is one of the main focuses of the paper. In our motivating data, the intercourse observations are a long series of binary data with a periodic probability of success and the amount of available intercourse data is a function of both the menstrual cycle length and TTP. Moreover, these variables are dependent and observed on different, and nested, timescales (TTP is measured in menstrual cycles whereas intercourse is measured on days within a menstrual cycle) further complicating its analysis. Here, we propose a semiparametric shared parameter model for the joint modelling of the binary longitudinal data (intercourse behaviour) and the discrete survival outcome (TTP). Further, we develop couple-based dynamic predictions for the intercourse profiles, which in turn are used to assess the risk for subfertility (i.e. TTP longer than six menstrual cycles).

Adverse childhood event experiences, fertility difficulties and menstrual cycle characteristics

INTRODUCTION

Increased childhood adversity may be affect adult fertility, however, the mechanism through which this occurs is unclear. Menstrual cycle abnormalities are predictive of fertility difficulties, and stress influences menstrual cycle characteristics. Here, we assess whether adverse childhood experiences (ACEs) are associated with fertility difficulties and menstrual cycle dysregulation, offering a plausible mechanism for the link between lifetime stress and fertility.

METHODS

From April 2012 to February 2014, 742 pregnant and non-pregnant women aged 18-45 years residing in southeastern Louisiana provided information on childhood adversity and reproductive history. Associations between ACEs and fertility difficulties and menstrual cycle patterns were evaluated.

RESULTS

As the number of ACEs increased, risk of fertility difficulties and amenorrhea increased (RR = 1.09, 95% CI 1.05-1.13 and RR = 1.07, 95% CI 1.04-1.10, respectively), while fecundability decreased [fecundability ratio (FR) = 0.97, 95% CI 0.95-1.00]. Compared to women with no adversity, women in the high adversity group were more likely to experience both infertility and amenorrhea (RR = 2.75, 95% CI 1.45-5.21 and RR = 2.54, 95% CI 1.52-4.25, respectively), and reduced fecundability (FR = 0.75, 95% CI 0.56-1.00). Although similar patterns were seen for menstrual cycle irregularity, associations were diminished. Associations did not materially change following adjustment for age, body mass index, race, education, smoking and income. Results are constrained by the self-report nature of the study and the limited generalizability of the study population.

DISCUSSION

To our knowledge, this is the first study to present evidence of a link between childhood stressors, menstrual cycle disruption and fertility difficulties. The effect of childhood stress on fertility may be mediated through altered functioning of the HPA axis, acting to suppress fertility in response to less than optimal reproductive circumstances.

Urinary follicle-stimulating hormone as a measure of natural fertility in a community cohort

High serum follicle-stimulating hormone (FSH) levels have been associated with diminished ovarian reserve; however, the association between high urinary FSH and reduced natural fertility has yet to be established. We sought to characterize the relationship between a single or multiple measurements of early follicular phase urinary FSH and fertility. Women (n = 209), 30 to 44 years old with no history of infertility, who had been trying to conceive for less than 3 months, provided early follicular phase urine. Participants subsequently kept a diary to record bleeding and intercourse and conducted standardized pregnancy testing for up to 6 months. A subset of women (N = 95) collected urine on cycle day 3 for up to 6 cycles. Urine was analyzed for FSH and creatinine (cr) corrected. Proportional hazard models were used to calculate fecundability ratios (FRs). Urinary FSH levels across cycles from the same woman were highly correlated (adjusted intraclass correlation = .77); within-woman variance was 3-fold lower than variance among women. Women with an initial urinary FSH level <7 mIU/mg cr exhibited a nonsignificant reduction in the probability of pregnancy (adjusted FR 0.71, 95% confidence interval [CI]: 0.45-1.13), as did women with elevated urinary FSH (≥12 mIU/mg cr; adjusted FR 0.78, 95% CI: 0.46-1.32). Using the most recent or maximum urinary FSH value did not strengthen the association. In the general population, urinary FSH levels appear to be nonlinearly associated with fertility; however, broad CIs indicate a lack of statistical significance. Repetitive testing appears to be of little benefit.

Assessing gonadal function after childhood ovarian surgery

PURPOSE

We aimed to assess the late effects of ovarian salvage or oophorectomy on gonadal function and fertility as measured by menstrual regularity.

METHODS

We performed a 10-year retrospective review of females aged 20 years or younger who required surgery to treat an ovarian disorder. A mail survey was distributed to these patients to evaluate the effects of ovarian surgery on menarche, menstrual regularity, and pregnancy.

RESULTS

A total of 180 females had surgery to treat an ovarian disorder. Eighty-six of these underwent unilateral oophorectomy (48%), whereas 94 (52%) had an ovary sparing procedure. Eighty-one patients (45%) returned completed surveys. Of the respondents, 44 had oophorectomy, and 37 had ovarian salvage. Ages of menarche were similar between surgical groups. Symptoms of menstrual irregularity differed most significantly according to painful menses (oophorectomy, 27.3%; salvage, 59.5%; P < .04). Interestingly, continuation of regular menses after surgery was higher in the oophorectomy group (oophorectomy, 70%; salvage, 15%; P = .013).

CONCLUSIONS

Unilateral oophorectomy does not appear to impair late gonadal function when compared with ovarian salvage. Surprisingly, oophorectomy appears to maintain more normal ovarian activity as estimated by menstrual regularity. Oophorectomy may be performed without apparent adverse effect on gonadal activity.

Persistent organochlorine pollutants and menstrual cycle characteristics

An evolving body of evidence suggests an adverse relation between persistent organochlorine pollutants (POPs) and menstruation, though prospective longitudinal measurement of menses is limited and served as the impetus for study. We prospectively assessed the relation between a mixture of persistent organochlorine compounds and menstrual cycle length and duration of bleeding in a cohort of women attempting to become pregnant. Eighty-three (83%) women contributing 447 cycles for analysis provided a blood specimen for the quantification of 76 polychlorinated biphenyls and seven organochlorine pesticides, and completed daily diaries on menstruation until a human chorionic gonadotropin confirmed pregnancy or 12 menstrual cycles without conception. Gas chromatography with electron capture detection was used to quantify concentrations (ng g(-1)serum); enzymatic methods were used to quantify serum lipids (mg dL(-1)). A linear regression model with a mixture distribution was used to identify chemicals grouped by purported biologic activity that significantly affected menstrual cycle length and duration of bleeding adjusting for age at menarche and enrollment, body mass index, and cigarette smoking. A significant 3-d increase in cycle length was observed for women in the highest tertile of estrogenic PCB congeners relative to the lowest tertile (β=3.20; 95% CI 0.36, 6.04). A significant reduction in bleeding (<1 d) was observed among women in the highest versus lowest tertile of aromatic fungicide exposure (γ=-0.15; 95% CI -0.29, -0.00). Select POPs were associated with changes in menstruation underscoring the importance of assessing chemical mixtures for female fecundity.